The present invention relates to a device which controls electric potential on the surface of photoconductive member for use in an image forming apparatus of electrophotographic copying machines, laser beam printers and the like, and more particularly to a device which controls electric potential on the surface of photoconductive member by controlling output of charging means.
Heretofore, various devices have been introduced as a mode of charging means which provide the surface of photoconductive member with uniform density of electric charge by impressing high voltage on charging wires thereby generating corona discharge.
However, a photoconductive member which encounters great light fatigue and possesses attenuation characteristic like the one provided with selenium as photoconductive member can not regularize charged electric potential in the area of developing process even if uniform density of electric charge is given in the process of electrification since the power for maintaining the electric charge decreases corresponding to light fatigue.
Accordingly, a control device is disclosed, for example, in Japanese Published Examine Patent Application No. 37500/l984. The device is arranged to stabilize the power of maintaining electric charge at a lower value by exposing a photoconductive member uniformly prior to image formation while taking longer exposure time according to the time the device is left in active for image forming process.
However, prior to image forming operation, preliminary treatment for photoconductive sensitivity adjustment is done after a print switch is turned on, by which the time required for image formation varies depending how long the device suspended its action. Especially when there was a long suspension of machine operation, a considerably longer period of time is required for the first image forming operation.